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Structural characterization and electrical conductivity analysis of MoO3–SeO2–ZnO semiconducting glass nanocomposites
摘要： A series of glass nanocomposite samples of the general composition formula xMoO3–(1-x) (0.5SeO2–0.5ZnO) for x = 0.05, 0.1, 0.2, and 0.3 have been prepared by solid-state reaction, i.e., slow cooling process. The structural characteristics have been explored by analyzing X-ray di?raction patterns, Fourier-transform infrared, and UV–Vis spectra. The superposition of di?erent nanophases SeO2, SeO3, ZnO, MoO3, Zn (SeO3), Zn (SeO4), Zn (MoO4), Zn2Mo3O8 and ZnMo8O10 over the amorphous glassy matrices have been identi?ed, and their crystallite sizes have been evaluated as well. Fourier transform infrared (FTIR) spectra reveal di?erent types of bonding like Zn–O–Se type and stretching vibrations of MoO6 octahedral units. It is observed that with increasing MoO3 concentration, the estimated values of optical bandgap energy, Urbach energy, and average crystallite size reduce. The dependency of electrical conductivity on frequency and temperature have been analyzed using Almond-West formalism and Jonscher's universal power-law. The non-linear character of DC conductivity and di?erent activation energies at low and high-temperature regions a?rm that the present glassy systems exhibit semiconducting nature. Moreover, DC conduction process is due to small polaron hopping through localized or defect states. The decreasing trend of power-law exponent (s) with temperature rise reveals that AC conduction mechanism is consistent with the correlated barrier-hopping (CBH) model. The existing correlated barrier-hopping model has been modi?ed to attain reasonable values of ?tting parameters and to obtain theoretical values of ideal thermodynamic glass transition temperature. The AC conductivity activation energy and free energy required for small polaron migration reduce with increasing conductivity. The scaling property emphasizes that conductivity relaxation process is subjected to the structure of the composition and does not depend on temperature.
关键词： XRD,UV–vis spectroscopy,Glass nanocomposites,Correlated barrier hopping model,DC and AC conductivity,FTIR
更新于2025-11-14 17:28:48
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Optical responses of BSA protein under re-entrant condensation in presence of trivalent ions
摘要： Fluorescence behavior of globular protein like BSA is studied under the re-entrant condensation in the presence of trivalent salts like YCl3 and LaCl3. BSA shows a re-entrant behaviour in solution where a specific turbid phase is formed between the two critical concentrations of the trivalent salts. Optical behaviours of proteins are explored by UV-Vis, photoluminescence and time resolved photoluminescence (TRPL) spectroscopy, whereas hydrodynamic size is obtained from the dynamic light scattering (DLS) technique. BSA shows maximum emission intensity at ≈ 338 nm for an excitation at 278 nm, however, the value of the peak intensity of emission gradually increases with the increase in salt concentration and becomes maximum at the turbid phase but for higher salt concentration as the re-dissolution takes place the emission intensity again decreases. TRPL study suggests that the decay time of BSA under re-entrant condensation is correlated with the salt concentration, whereas DLS study shows that the hydrodynamic size gradually increases up to a certain salt concentration where turbid phase is formed and then again decreases for higher salt concentrations. The variation of emission intensity of BSA nearly follows the modification of diffusion coefficient or hydrodynamic size and the phase transition behaviours.
关键词： UV-Vis spectroscopy,Bovine serum albumin,Tri-valent ions,Re-entrant condensation,Fluorescence spectroscopy
更新于2025-09-23 15:23:52
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Fraction of Rare-Earth (Sm/Nd)-Lanthanum Ferrite-Based Perovskite Ferroelectric and Magnetic Nanopowders
摘要： Multiferroic compound, especially LaFeO3-based perovskite nanopowders that exhibit robust simultaneous ferromagnetism and ferroelectricity, are widely investigated and applied in different applications. In this work, we report the synthesis and characterization pertaining to fraction of rare-earth (Sm/Nd)-substituted lanthanum ferrite based perovskite nanopowders via solid-state technique. The multiferroic phenomenon is the fundamental approach to combine both the ferromagnetic and ferroelectric properties in a single system. Reduction in crystallite size, as well as some lattice distortion effects, are included to show the possibilities of tuning the lattice structure, electrical, optical as well as the magnetic properties which are closely connected to the ferroelectric behavior and magnetism. At room temperature, the ferroelectric behavior of La0.9(Sm/Nd)0.1FeO3 exhibiting a P-E hysteresis loop became more and more pronounced, indicating the electrical leakage is greatly reduced. The canted antiferromagnetic hysteresis loop shows that the rare-earth (Sm/Nd) ion can significantly affect the magnetic parameters of the materials.
关键词： Lanthanum ferrite,x-ray diffraction,optical and magnetic properties,solid-state reaction,ferroelectric,UV–Vis spectroscopy
更新于2025-09-23 15:23:52
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Optical spectroscopy of the Au4+ cluster: Resolved vibronic structure indicates an unexpected isomer**
摘要： The knowledge of the geometric and electronic structure of gold clusters and nanoparticles is vital for understanding their catalytic and photochemical properties at the molecular level. Herein, we report the vibronic optical photodissociation spectrum of cold and mass-selected Au4+ clusters measured at a resolution high enough to allow for comparison with Franck-Condon simulations of the excited state transitions based on time-dependent density functional theory calculations. The three vibrational frequencies identified for the lowest-lying optically accessible excited state at 2.17 eV stem from the Y-shaped isomer (C2v) and not from the rhombic isomer (D2h) that is considered to be the ground state structure of Au4+. This study demonstrates that an analysis of low-resolution electronic spectra by calculations of vertical transitions alone is not sufficient for a reliable isomer assignment of such metal clusters.
关键词： gold,UV/Vis spectroscopy,structure elucidation,cluster compounds,electronic structure
更新于2025-09-23 15:23:52
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Structural, energetic and spectroscopic studies of new luminescent complexes based on 2-(2′-hydroxyphenyl)imidazo[1,2- <i>a</i> ]pyridines and 1,2-phenylenediboronic acid
摘要： Three new blue-luminescent complexes of selected imidazo[1,2-a]pyridine derivatives and 1,2-phenylenediboronic acid have been synthesized and structurally characterized using single-crystal X-ray diffraction. Additionally, the crystal structures of two of the (N,O)-donor compounds have been evaluated for the first time. The crystal packing and molecular motifs observed in the studied crystals have been thoroughly analysed, including computational studies, and are also discussed within the context of analogous systems reported in the literature. It appears that the new compounds form different crystal networks with regard to the asymmetric unit content and packing, although some similarities can be found. In all cases a typical centrosymmetric dimer bound via boronic acid groups is formed, characterized by an interaction energy of about -80 kJ mol-1, while the 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine complex and its methoxy derivative form solvate structures, somewhat resembling the previously studied 8-oxyquinolinate analogues. As far as the spectroscopic properties are concerned, the lowest energy excitation observed in the studied complexes is based on the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, and both these molecular orbitals are centred predominantly on the (N,O)-donor species according to the results of time-dependent density functional theory. Thus, the charge transfer observed for the 8-oxyquinolinate equivalents does not occur in these cases. Consequently, the spectroscopic behaviour of the series is very much comparable with that of the parent imidazo[1,2-a]pyridine derivatives, if the excited-state intramolecular proton-transfer process does not take place, as shown by the absorption and emission spectra collected in toluene and acetone solutions. Complexation causes a reduction in the Stokes shift compared with the respective (N,O)-donor molecules.
关键词： periodic calculations,TDDFT,UV–Vis spectroscopy,X-ray diffraction,time-dependent density functional theory,spectroscopic properties,luminescent boron complexes,transferred aspherical atom model (TAAM) refinement
更新于2025-09-23 15:22:29
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Photo-Annealing of Merocyanine Aggregates
摘要： In this work we elucidate the fundamental difference between aggregate formation of donor-π-acceptor merocyanines in their electronic ground and excited states. While increasing the π-bridge size favors formation of π-stacked aggregates in the dark, irradiation with visible light causes reorientation of the dyes to form prototype H-aggregates with compensating dipole moments. This photo-annealing changes the supramolecular structure and its UV-vis spectroscopic properties dramatically, thus being of importance for the function of active layers composed of these dyes. Aggregates of the ground state dyes are bound cooperatively through ππ-London dispersion interactions and hydrogen bonds between the polar α-cyano-carboxylic acid groups. However, charge transfer upon photoexcitation leads to repulsion of the polar acid groups. Electronic excitation of the dyes approximately doubles the ground state dipole moment, thus driving molecular reorientation into prototype H-aggregate structures. We show that this photo-induced supramolecular rearrangement can disrupt the large polymeric aggregates formed in the dark. The photo-induced supramolecular structural changes reported in this work will influence the performance of optoelectronic devices composed of these structures and must be controlled to avoid morphological decomposition of active layers upon operation.
关键词： merocyanines,photo-annealing,H-aggregates,supramolecular structure,UV-vis spectroscopy,dipole moments,aggregate formation
更新于2025-09-23 15:21:21
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Characterizing Molecular Adsorption on Biodegradable MnO <sub/>2</sub> Nanoscaffolds
摘要： Biodegradable MnO2 nanoscaffolds have recently been designed for advanced stem cell therapy. These nanomaterials strongly bind extracellular matrix proteins and effectively deliver therapeutic molecules, which significantly enhance stem cell survival and neuronal differentiation both in vitro and in vivo. In this work, we combine molecular dynamics simulations, density functional theory calculations and UV-Vis spectroscopy experiments to examine the selectivity and efficiency of a MnO2 nanosheet in adsorbing neurogenic drugs. To uncover the fundamental principles governing the drug loading process, we have systematically examined a series of model aromatic and alkyl compounds with characteristic functional groups and demonstrated that molecular adsorption on the MnO2 nanosheet results from an interplay of dispersion, electrostatic and charge transfer interactions. We have then proposed a metric that efficiently predicts the qualitative adsorption affinity of a guest molecule on the MnO2 nanosheet based on its structural and chemical features, which will facilitate the experimental screening of proper adsorbates for efficient molecular delivery and aid the development of MnO2-based nanoscaffolds for biomedical applications.
关键词： adsorption affinity,molecular dynamics simulations,density functional theory,MnO2 nanoscaffolds,neurogenic drugs,UV-Vis spectroscopy
更新于2025-09-23 15:21:21
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Tenfold increase in the photostability of an azobenzene guest in vapor-deposited glass mixtures
摘要： Improvements to the photostability of organic glasses for use in electronic applications have generally relied on the modification of the chemical structure. We show here that the photostability of a guest molecule can also be significantly improved—without chemical modification—by using physical vapor deposition to pack molecules more densely. Photoisomerization of the substituted azobenzene, 4,4'-diphenyl azobenzene, was studied in a vapor-deposited glass matrix of celecoxib. We directly measure photoisomerization of trans- to cis-states via Ultraviolet-visible (UV-Vis) spectroscopy and show that the rate of photoisomerization depends upon the substrate temperature used during co-deposition of the glass. Photostability correlates reasonably with the density of the glass, where the optimum glass is about tenfold more photostable than the liquid-cooled glass. Molecular simulations, which mimic photoisomerization, also demonstrate that photoreaction of a guest molecule can be suppressed in vapor-deposited glasses. From the simulations, we estimate that the region that is disrupted by a single photoisomerization event encompasses approximately 5 molecules.
关键词： photostability,organic glasses,azobenzene,photoisomerization,physical vapor deposition,molecular simulations,UV-Vis spectroscopy
更新于2025-09-23 15:21:21
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Fluorescence quenching of molybdenum disulfide quantum dots for metal ion sensing
摘要： In the present work, we have used hydrothermally synthesized in situ functionalized MoS2-QDs for a sensitive (limit of detection ~ 2.06 μM) and selective detection of Fe3+ ions. A detailed study of fluorescence quenching behavior for MoS2-QDs in the presence of Fe3+ ions has been performed using the Stern–Volmer plot, modified Stern–Volmer plot, and time-resolved photoluminescence measurements. Absorption based titration spectra and time-resolved photoluminescence measurements confirmed the fluorescence quenching is static with three decay times originated from the three different fluorescing sites. Interestingly, it is found that emission spectra consist of three bands at positions ~ 450 nm (P1, ~ 2.76 eV), ~ 475 nm (P2, ~ 2.61 eV), and ~ 503 nm (P3, ~ 2.46 eV). These peaks show a systematic quenching with the increasing concentration of Fe3+ ions. Quenching constants corresponding to these emission bands are found of the order of ~ 103 M?1. Large values of bimolecular quenching constants (~ 1011 M?1 s?1) suggest a strong binding interaction between MoS2-QDs and Fe3+ ions. Furthermore, to understand the fluorescence quenching of MoS2-QDs in the presence of Fe3+ ions, a ground-state complex formation-based mechanism has been proposed and elucidated in detail.
关键词： Nanostructures,UV/Vis spectroscopy,Metal ion sensing,Time-resolved photoluminescence,Fluorescence spectroscopy
更新于2025-09-23 15:21:01
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Physicala??Chemical Properties of Self-Assembled Structures in Solution of Zinc Phthalocyanine and Bis-3-pentyl-PTCDI Derivative
摘要： For the first time, in this work, we succeed in synthesizing in solution a novel supramolecular self-assembled zinc phthalocyanine (ZnPc) and N,N′-bis(3-pentyl)-perylene-3,4,9,10-bis(dicarboximide) (bis-3-pentyl-PTCDI) system with improved light absorption and phosphorescence lifetime of the charge separated states up to 2.5 ms. Moreover, the structural and optical properties of undoped and doped with iodine ZnPc thin films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman analysis, and UV?vis spectroscopy. Analysis of ZnPc:I2:bis-3-pentyl-PTCDI blend in a 2:1 ratio shows that sandwich complexes between them result in improved bulk properties as compared to those of the single-component systems.
关键词： light absorption,Fourier transform infrared spectroscopy,UV?vis spectroscopy,bis-3-pentyl-PTCDI,X-ray diffraction,supramolecular self-assembly,X-ray photoelectron spectroscopy,zinc phthalocyanine,phosphorescence lifetime,Raman analysis
更新于2025-09-23 15:19:57